Integral bit retention system

ABSTRACT

A percussion bit assembly includes a percussion bit having an upper, elongated bit shank, a lower bit head, and a bit skirt disposed intermediate the bit shank and the bit head. The percussion bit has an axial bore extending longitudinally through at least the bit shank and the bit skirt and at least one receptacle extending radially outward from the lower portion of the axial bore. A bit retainer includes at least one longitudinal member and at least one lateral member. The longitudinal member extends longitudinally within the axial bore of the percussion bit from an upper end portion, mounted within the upper portion of the axial bore, to a lower end portion disposed in the lower portion of the axial bore. The lateral member extends laterally from a radially inner end portion connected to the lower end portion of the longitudinal member to a radially outer end portion mounted in the receptacle.

BACKGROUND OF THE INVENTION

This invention relates generally to earth boring percussion bits. More particularly, the invention relates to retention systems for ensuring that even when broken during use, the percussion bit remains connected to the drill string.

U.S. Pat. No. 5,065,827 discloses a conventional hammer and percussion bit assembly having a percussion bit retention system. The percussion bit retention system includes a retainer which is mounted on the drive sub of the percussion bit assembly. The retainer includes a lower section having an inner chamber and a thread-shaped, inwardly extending projection. The bottom portion of the percussion bit includes a head section, a threaded section and a recess disposed intermediate the head section and the threaded section. The percussion bit is installed by inserting the upper portion of the percussion bit into the retainer until the threaded section of the lower portion abuts the thread-shaped projection of the retainer. The projection is brought into threaded engagement with the threaded section of the retainer and the retainer is rotated until the projection passes completely through the threaded section of the retainer and enters the chamber. If the percussion bit breaks in the shaft portion above the bottom portion of the percussion bit, the projection will be captured within the chamber by the threaded section of the retainer.

The threaded section of such retainers may become fouled during drilling operations, making removal of the percussion bit difficult. Bits may be difficult to install due to corrosion and wear induced degradation of the threaded section of the retainer.

U.S. Pat. No. 6,070,678, discloses a bit retention system having a substantially tubular retainer member. The retainer member has a bore of substantially uniform internal diameter which can slip over the retention shoulder of the percussion bit, whether that shoulder is solid or threaded. Pins are then driven through holes in the retainer, under the retention shoulder. The pins retain the head of the bit in the event of bit breakage. Although this bit retention system eliminates many of the problems associated with threaded bit retention systems of the type described above, the system requires modification of the chuck. Accordingly, the system cannot be used until a modified chuck is installed on the drill string.

SUMMARY OF THE INVENTION

With the present invention, a novel percussion bit assembly, and associated novel bit retainer, can be simply achieved without the requirement for rotating the bit relative to the retainer, and without the risk of thread fouling.

In accordance with the invention, a percussion bit assembly comprises a percussion bit having an upper, elongated bit shank, a lower bit head, and a bit skirt disposed intermediate the bit shank and the bit head. The percussion bit has an axial bore extending longitudinally through at least the bit shank and the bit skirt and at least one receptacle extending radially outward from the lower portion of the axial bore. A bit retainer includes at least one longitudinal member and at least one lateral member. The longitudinal member extends longitudinally within the axial bore of the percussion bit from an upper end portion, mounted within the upper portion of the axial bore, to a lower end portion disposed in the lower portion of the axial bore. The lateral member extends laterally from a radially inner end portion connected to the lower end portion of the longitudinal member to a radially outer end portion mounted in the receptacle.

The upper portion of the percussion bit axial bore forms a circumferential shelf. In one embodiment, the bit retainer includes a pair of retainer bars, with each of the retainer bars having a longitudinal portion and a lateral portion defining the longitudinal and lateral members. A radially outer end portion of each lateral portion is received in one of a pair of circumferentially spaced receptacles. The upper end portion of each longitudinal portion has a tab extending radially outward therefrom which are supported on the shelf of the percussion bit axial bore. The bit retainer also includes upper and lower spacers. The upper spacer is positioned proximate to the upper end portions of the retainer bars and the lower spacer is positioned proximate to the lower end portions of the retainer bars, such that the upper and lower spacers prevent radial movement of the tabs and the lateral portion of the retainer bars.

The lower end portion of each retainer bar includes a protrusion extending radially inward into the axial bore, with the lower spacer being supported on the protrusions of the retainer bars. The lower spacer is an H-shaped member forming a pair of oppositely disposed indentations and an axial opening. The lower end portion of one of the retainer bars is received in each of the indentations.

The upper spacer is a substantially cylindrical member, having a wall forming an axial opening and a pair of oppositely disposed indentations extending radially inward into the opening. The upper end portion of the longitudinal portion of one of the retainer bars is received in each of the indentations. The upper spacer is supported on the shelf of the percussion bit axial bore.

In another embodiment, the receptacle is a transverse bore extending from the outer surface on a first side of the bit skirt, through the axial bore, and into an opposite, second side of the bit skirt. The longitudinal member is a retainer tube having a lower end portion with oppositely disposed openings. The upper end portion of the retainer tube has a radially extending circumferential collar which is supported on a shelf formed in the upper portion of the percussion bit bore. The lateral member is a pin having a first end portion positioned in a segment of the transverse bore in the first side of the bit skirt, a middle portion extending through the openings of the retainer tube lower end portion, and a second end portion positioned in a segment of the transverse bore in the second side of the bit skirt.

In one variation of this embodiment, the first end portion of the pin includes outer and inner segments. The outer segment extends from the outer surface of the first side of the bit skirt to an intermediate position between the outer surface of the first side of the bit skirt and the axial bore, with the inner segment extending from the intermediate position to the axial bore. The second end and middle portions of the pin and the inner segment of the first end portion of the pin have a substantially uniform outside diameter which is smaller than the inside diameters of the transverse bore and the openings of the retainer tube, to facilitate insertion of the pin into the transverse bore. The outer segment of the first end portion of the pin has an outside diameter selected such that the outer segment frictionally engages the transverse bore after the pin is inserted.

In a second variation of the embodiment, the segment of the transverse bore in the first side of the bit skirt includes outer and inner portions, with the outer portion extending from the outer surface of the first side of the bit skirt to an intermediate position between the outer surface of the first side of the bit skirt and the axial bore. The pin has a substantially uniform outside diameter which is smaller than the inside diameters of the transverse bore and the openings of the retainer tube, to facilitate insertion of the pin into the transverse bore. The first end portion of the pin is disposed in the transverse bore segment inner portion and a plug is fixedly mounted in the transverse bore segment outer portion.

In still another embodiment, the receptacle is a transverse bore which extends radially through the bit skirt, having a first segment extending from the outer surface on a first side of the bit skirt to the axial bore and a second segment extending from the axial bore to the outer surface on an opposite, second side of the bit skirt. The longitudinal member is a retainer tube having a lower end portion with oppositely disposed openings. The lateral member is substantially identical first and second pins, each having outer and inner segments. The inner segment of each pin has an outside diameter which is smaller than the inside diameters of the transverse bore and the openings of the retainer tube while the outer segment of each pin has an outside diameter selected such that the outer segment frictionally engages the transverse bore after the pin is inserted. The first and second pins are disposed in the first and second segments of the transverse bore, with the outer segment of each pin extending from the outer surface of the bit skirt to an intermediate position between the outer surface of the bit skirt and the axial bore and the inner segment extending from the intermediate position through a one of the openings of the retainer tube.

It is thus an object of the invention to provide a new and improved retention system for a percussion bit assembly.

It is also an object of the invention to provide a retention system for a percussion bit assembly that is self-contained within the percussion bit.

Other objects and advantages of the invention will become apparent from the drawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing in which:

FIG. 1 is an elevation view, partly in section and partly in phantom, of a conventional hammer-percussion bit assembly;

FIG. 2 is a simplified, enlarged view, partly in section and partly in phantom, of the lower end portion of a hammer-percussion bit assembly according to a first embodiment of the invention;

FIG. 3 is an enlarged top view of the upper spacer of FIG. 2;

FIG. 4 is an enlarged top view of the lower spacer of FIG. 2;

FIG. 5 is a side view of the retainer bar of FIG. 2;

FIG. 6 is a simplified, enlarged view, partly in section and partly in phantom, of the lower end portion of the hammer-percussion bit assembly according to a second embodiment of the invention;

FIG. 7 is a simplified, enlarged view, partly in section and partly in phantom, of the lower end portion of the hammer-percussion bit assembly according to a third embodiment of the invention;

FIG. 8 is a simplified, enlarged view, partly in section and partly in phantom, of the lower end portion of the hammer-percussion bit assembly according to a fourth embodiment of the invention;

FIG. 9 is a simplified, enlarged view, partly in section and partly in phantom, of the lower end portion of the hammer-percussion bit assembly according to a fifth embodiment of the invention;

FIG. 10 is a simplified, enlarged view, partly in section and partly in phantom, of the lower end portion of the hammer-percussion bit assembly according to a sixth embodiment of the invention;

FIG. 11 is an enlarged cross section view taken along line XI-XI of FIG. 9;

FIG. 12 is an enlarged cross section view taken along line XII-XII of FIG. 10; and

FIG. 13 is a simplified, enlarged view, partly in section and partly in phantom, of the lower end portion of the hammer-percussion bit assembly according to a seventh embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A hammer-percussion bit assembly 10 with a conventional bit retention system 12, is shown in FIG. 1. The percussion bit assembly comprises a hammer housing 14 threadably connected at its upper end portion 16 to a drill string mounting member 18. An opening in the lower end 20 of the housing 14 receives the upper portion 22 of tubular chuck member 24 and is threadably connected thereto.

A lock cylinder 26 and a split lock ring 28 are positioned within the interior of the housing 14. The upper portion 30 of the percussion bit shank 32 is disposed within the lock ring 28 and lock cylinder 26 such that an upper radially extending shoulder 34 on the upper portion 30 is positioned within the lock cylinder 26 and above the lock ring 28. The inside diameters of the lock cylinder 26 and the lock ring 28 and the outside diameter of the upper shoulder 34 are selected such that the upper shoulder 34 is free to move up and down within the lock cylinder 26 and is captured by the lock ring 28.

The upper portion 30 of the percussion bit shank 32 also includes an upper bearing surface 36. The percussion bit shank 32 has a lower bearing surface 38 adapted for bearing against the lower surface 40 of the chuck member 24. The bottom surface 42 of the hammer impact piston 44 impacts against the upper bearing surface 36 to impart a percussive force to the bit 46. Alternatively, the percussive force may be transmitted through the lower surface 40 of the chuck member 24 to the lower bearing surface 38 of the bit 46.

A percentage of all percussion bits shanks 32 fail due to cyclic fatigue by fracturing below the lock ring 28 and above the bit head 48. When this occurs during the drilling operation, the lower section of the percussion bit is left at the bottom of the hole, requiring a costly and cumbersome fishing operation.

Percussion bit retention system 12 employs a cylindrical retainer member 50 disposed around the lower portion 52 of the chuck member 24 and the shoulder 54 of the bit 46. A pair of pins 56 are insertable through a pair of holes in the lower portion of the retainer member 50 below the shoulder 54 of the bit 46. A longitudinal channel is defined between the upper end of retainer member 50 and the pair of pins 56, having a length selected to receive the lower portion 52 of the chuck member 24 and to allow free vertical movement of the lower shoulder 54 of the percussion bit 46. In the event of breakage of the bit shank 32 above the bit shoulder 54, the shoulder 54 engages the pins 56 to retain the broken bit.

A bit retention system 58, 106, 118, 126, 138, 140, 198 in accordance with the invention is integral with the bit 60. Accordingly, such a bit 60 may be used with any standard drill without requiring modification of the drill. With reference to FIGS. 2-5, a first embodiment of a bit retention system 58 in accordance with the invention includes a pair of retainer bars 62 and upper and lower spacers 64, 66.

Each retainer bar 62 has an upper end portion 68 including a radially extending tab 70, an intermediate portion 72 extending downwardly from upper end portion 68, and a radial retainer portion 74 extending perpendicularly from the intermediate portion 72. The bottom end of intermediate portion 72 includes a radially extending protrusion 76. The retainer bars 62 are inserted longitudinally into the upper end 78 of the bit axial bore 80, retainer portion 74 first, until the lower surface 82 of each tab 70 is positioned just above the location of a shelf 84 formed in bore 80 and each retainer portion 74 is positioned proximate to a receptacle 86, 86′ in extending radially outward from bore 80. Receptacle 86 is positioned 180 degrees from receptacle 86′. The retainer bars 62 are urged radially outward such that the retainer portions 74 are inserted into the receptacles 86, 86′, whereby the retainer bars 62 are positioned on opposite sides of bore 80, and the tabs 70 are positioned above shelf 84.

The lower spacer 66 is an H-shaped member (with the H laying on its side) having a pair of oppositely disposed indentations 88 and an axial opening 90. The lower spacer 66 is inserted through the upper end 78 of bore 80, with a retainer bar 62 sliding through each of the indentations 88, until the lower surface 92 of the lower spacer 66 rests on the retainer bar protrusions 76, thereby locking each retainer portion 74 within the corresponding receptacle 86, 86′. The H-shape of the lower spacer 66 and the opening 90 provides sufficient mechanical strength to hold the retainer portion 74 of each retainer bar 62 in position while minimizing interference with flow through bore 80.

The upper spacer 64 is substantially cylindrical, having a wall 94 forming an axial opening 96 and having a pair of oppositely disposed indentations 98 extending radially inward into the opening 96. The upper spacer 64 is inserted into the upper end 78 of bore 80 such that the upper end portion 68 of each retainer bar 62 is received in one of the indentations 98, thereby locking upper end portion 68 in radial position, and the lower surface 100 of the upper spacer 64 rests on shelf 84. An exhaust tube 102 is then mounted within the upper end of bore 80 to prevent longitudinal movement of the upper spacer 64. The wall 94 has a thickness selected to provide sufficient mechanical strength to hold the upper end portion 68 of each retainer bar 62 in position while minimizing interference with flow through bore 80.

Shelf 84 is located on the bit shank 103 and receptacles 86, 86′ are located in the skirt 104 of bit head 105. It should be appreciated that substantially all of the bit shank failures described above occur in the portion of the bit shank 103 located between these two locations. It should also be appreciated that while the upper and lower spacers 64, 66 lock the retainer bars 62 in position, the retainer bars 62 are not so rigidly mounted to the bit 107 that they are subjected to the impact stress experienced by the bit 107. Accordingly, the majority of broken bits will be retained by the subject bit retention system 58.

In a second embodiment of the bit retention system 106 (FIG. 6), the upper end and intermediate portions 68, 72 of the retainer bar 62′ are substantially identical to the upper end and intermediate portions 68, 72 of the retainer bar 62 of the first embodiment 58. However in this embodiment, the retainer portion 108 includes an upper segment 110 that extends downward, parallel to the intermediate portion 72, and a lower segment 112 that extends at an obtuse angle from the upper segment 110. The retainer portions 108 are received in oppositely disposed receptacles 114 which extend radially away from the bore axis 115 and longitudinally toward the face 116 of the bit head 105.

In a third embodiment of the bit retention system 118 (FIG. 7), the upper end portion 68 of the retainer bar 62″ is substantially identical to the upper end portion 68 of the retainer bar 62 of the first embodiment 58. However, the intermediate portion 120 is longer, extending further into the bit skirt 104 in the installed condition, and the retainer portion 122 extends at an acute angle from the intermediate portion 120. The retainer portions 122 are received in oppositely disposed pit-shaped receptacles 124 which extend longitudinally away from the face 116 of the bit head 105.

In a fourth embodiment of the bit retention system 126 (FIG. 8), the upper end and intermediate portions 68, 72 of the retainer bar 62′″ are substantially identical to the upper end and intermediate portions 68, 72 of the retainer bar 62 of the first embodiment 58. The retainer portion 128 extends at an obtuse angle from the intermediate portion 72. The retainer portions 128 are received in oppositely disposed receptacles 130 which extend radially away from the bore axis 115 and longitudinally toward the face 116 of the bit head 105. However, the angle 132 formed between retainer portion 128 and intermediate portion 72 is smaller than the angle 134 formed between the upper and lower segments 110, 112 of retainer portion 108 (FIG. 6). Since retainer portion 128 does not include the upper segment 110 of retainer portion 108, receptacles 130 may be formed by drilling holes from the outer surface 136 of the bit skirt 104.

In fifth, sixth and seventh embodiments of the bit retention system 138, 140, 198 (FIGS. 9-13), a single retainer tube 142 is used instead of the two retainer bars 62, 62′, 62″, 62′″. The upper end portion 144 of the tube 142 has a circumferential, radially extending collar 146 which has a lower surface 148 that rests on shelf 84. The tube 142 extends from upper end portion 144 to a lower end portion 150 disposed in the bit skirt 104. For embodiments 138 and 140, a single blind bore 152 extends from the outer surface 136 of the bit skirt 104, through the first side 154 of the bit skirt 104, through the bit bore 80 and partially through the second side 156 of the bit skirt 104. In embodiment 198, oppositely disposed bores 200 extend from the outer surface 136 of the bit skirt 104, through each of the first and second sides 154, 156 of the bit skirt 104, to the bit bore 80. When installed, a pair of oppositely disposed openings 158 in the lower end portion 150 of the tube 142 align with the blind bore 152/bores 200. The upper end portion 144 of the tube 142 is locked to the upper bit shank 103 by the exhaust tube 102 and the lower end portion 150 of the tube 142 is locked to the bit head 105 by a pin 160, 160′/pins 160″. In the fifth and sixth embodiments 138, 140 pin 160, 160′ extends from the outer surface 136 of the bit skirt 104, through the first side 154 of the bit skirt 104, through the bit bore 80. The second end portion 162 of the pin 160, 160′ is positioned in blind bore segment 164, the middle portion 166 is positioned within openings 158, and the first end portion 168, 168′ is positioned in the blind bore segment 170. In the seventh embodiment 198, each of the pins 160″ extends from the outer surface 136 of the bit skirt 104, through one of the sides 154, 156 of the bit skirt 104, with the middle portion 166″ extending through one of the openings 158 and partially into the bit bore 80.

In the embodiment 138 shown in FIGS. 9 and 11, the second end portion 162, the middle portion 166 and an inner segment 172 of the first end portion 168 have a uniform diameter 174 which is sufficiently smaller than the inside diameter 176 of blind bore 152 and openings 158 to allow easy passage therethrough. An outer segment 178 of the first end portion 168 has an outside diameter 180 which is greater than outside diameter 174. Diameter 180 is selected such that the outer surface 182 of outer segment 178 will frictionally engage the inner surface 184 of blind bore segment 170 to lock an installed pin 160 within blind bore 152. To install the pin 160, the bit skirt 104 is heated sufficiently to increase inside diameter 176, the pin 160 is inserted into blind bore 152, and the bit skirt 104 is allowed to cool. As the bit skirt cools, inside diameter 176 returns to its original size, thereby clamping the outer segment 178 of the pin 160 within blind bore segment 170. Any part of outer segment 178 which extends beyond the outer surface 136 of bit skirt 104 may be machined flush with the surface 136.

In the embodiment 140 shown in FIGS. 10 and 12, the entire pin 160′ has a uniform diameter 186 which is sufficiently smaller than the inside diameter 188 of blind bore 152 and openings 158 to allow easy passage therethrough. The pin 160′ has a length 190 that is less than the length 192 of blind bore 152. Accordingly, an outer portion 194 of bore segment 170 remains empty after the pin 160′ is fully inserted into blind bore 152. A plug or a plug weld 196 is installed in this outer portion 194 to lock the pin 160′ in blind bore 152.

The embodiment 198 shown in FIG. 13 is a variation of embodiment 138, with two pins 160″ and two bores 200 in place of the single pin 160 and blind bore 152 of embodiment 138. Preferably the bores 200 are positioned substantially 180° apart. Each pin 160″ has a first end portion 168 having an inner segment 172 and an outer segment 178, similar to pin 160. However, the middle portion 166″ of each pin 160″ only extends through one of the openings 158 and a short distance into retainer tube 142, preferably about ¼ inch. Neither pin 160″ has the second end portion 162 of pin 160. Similar to pin 160, the middle portion 166″ and the inner segment 172 of the first end portion 168 have a uniform diameter 174 which is sufficiently smaller than the inside diameter 202 of bore 200 and openings 158 to allow easy passage therethrough. The outer segment 178 of the first end portion 168 has an outside diameter 180 which is greater than outside diameter 174 such that the outer surface of outer segment 178 will frictionally engage the inner surface of bore 200 to lock an installed pin 160″ within bore 200. To install the pins 160″, the bit skirt 104 is heated sufficiently to increase inside diameter 202, one of the pins 160″ is inserted into each bore 200, and the bit skirt 104 is allowed to cool. As the bit skirt cools, inside diameter 176 returns to its original size, thereby clamping the outer segment 178 of the pins 160″ within the bores 200. Any part of outer segment 178 which extends beyond the outer surface 136 of bit skirt 104 may be machined flush with the surface 136. The pins 160″ of this embodiment 198 restrict the flow passage within the retainer tube 142 less than the pin 160 of embodiment 138.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation. 

1. A percussion bit assembly for downhole boring operations comprising: a percussion bit including an upper, elongated bit shank, a lower bit head, and a bit skirt disposed intermediate the bit shank and the bit head; the percussion bit defining an axial bore extending longitudinally through at least the bit shank and the bit skirt, the axial bore having upper and lower portions; the percussion bit also defining at least one receptacle extending radially outward from the lower portion of the axial bore; and a bit retainer including at least one longitudinal member and at least one lateral member; the longitudinal member extending longitudinally within the axial bore of the percussion bit from an upper end portion, mounted within the upper portion of the axial bore, to a lower end portion disposed in the lower portion of the axial bore; the lateral member extending laterally from a radially inner end portion, connected to the lower end portion of the longitudinal member, to a radially outer end portion mounted in the receptacle.
 2. The percussion bit assembly of claim 1 wherein the percussion bit defines first and second circumferentially spaced receptacles, the upper portion of the percussion bit axial bore defines a circumferential shelf, and the bit retainer includes a pair of retainer bars; each of the retainer bars including a longitudinal portion and a lateral portion defining the longitudinal and lateral members; a radially outer end portion of each lateral portion being received in one of the receptacles; the upper end portion of each longitudinal portion having a tab extending radially outward therefrom, the tabs being supported on the shelf of the percussion bit axial bore.
 3. The percussion bit assembly of claim 2 wherein the bit retainer also includes upper and lower spacers, the upper spacer being positioned proximate to the upper end portions of the retainer bars and the lower spacer being positioned proximate to the lower end portions of the retainer bars, whereby the upper and lower spacers prevent radial movement of the tabs and the lateral portion of the retainer bars.
 4. The percussion bit assembly of claim 3 wherein the lower end portion of each retainer bar includes a protrusion extending radially inward into the axial bore, the lower spacer being supported on the protrusions of the retainer bars.
 5. The percussion bit assembly of claim 4 wherein the lower spacer is an H-shaped member defining a pair of oppositely disposed indentations and an axial opening, the lower end portion of the longitudinal portion of one of the retainer bars being received in each of the indentations.
 6. The percussion bit assembly of claim 3 wherein the upper spacer is a substantially cylindrical member, having a wall defining an axial opening and a pair of oppositely disposed indentations extending radially inward into the opening.
 7. The percussion bit assembly of claim 6 wherein the upper end portion of the longitudinal portion of one of the retainer bars being received in each of the indentations,
 8. The percussion bit assembly of claim 7 wherein the upper spacer is supported on the shelf of the percussion bit axial bore.
 9. The percussion bit assembly of claim 1 wherein the at least one receptacle extends radially outward into the bit skirt.
 10. The percussion bit assembly of claim 1 wherein the at least one receptacle extends radially outward into the bit head.
 11. The percussion bit assembly of claim 1 wherein the at least one receptacle extends radially outward at an obtuse angle from the axial bore and lateral member extends at an obtuse angle from the lower end portion of the longitudinal member.
 12. The percussion bit assembly of claim 1 wherein the at least one receptacle extends radially outward at an obtuse angle from the axial bore and lateral member includes an upper segment that extends substantially parallel to the longitudinal member and a lower segment that extends at an obtuse angle from the upper segment.
 13. The percussion bit assembly of claim 12 wherein the at least one receptacle extends through the bit skirt into the bit head.
 14. The percussion bit assembly of claim 1 wherein the at least one receptacle extends radially outward at an acute angle from the axial bore and lateral member extends at an acute angle from the lower end portion of the longitudinal member.
 15. The percussion bit assembly of claim 1 wherein the bit skirt has an outer surface; the receptacle is a transverse bore extending from the outer surface on a first side of the bit skirt, through the axial bore, and into an opposite, second side of the bit skirt; the longitudinal member is a retainer tube having a lower end portion defining oppositely disposed, first and second openings; and the lateral member is a pin; the pin having a first end portion positioned in a segment of the transverse bore in the first side of the bit skirt, a middle portion extending through the openings of the retainer tube lower end portion, and a second end portion positioned in a segment of the transverse bore in the second side of the bit skirt.
 16. The percussion bit assembly of claim 15 wherein the upper portion of the percussion bit bore defines a circumferential shelf and a upper end portion of the retainer tube has a circumferential collar extending radially outward therefrom, the collar being supported on the shelf.
 17. The percussion bit assembly of claim 16 wherein the transverse bore and the openings of the retainer tube each have an inside diameter; the first end portion of the pin includes outer and inner segments, the outer segment extending from the outer surface of the first side of the bit skirt to an intermediate position between the outer surface of the first side of the bit skirt and the axial bore, the inner segment extending from the intermediate position to the axial bore; the second end portion of the pin, the middle portion of the pin, and the inner segment of the first end portion of the pin have a substantially uniform outside diameter which is smaller than the inside diameters of the transverse bore and the openings of the retainer tube, and the outer segment of the first end portion of the pin has an outside diameter selected for frictional engagement between the outer segment of the first end portion of the pin and the transverse bore.
 18. The percussion bit assembly of claim 16 wherein the bit retainer also includes a plug; the segment of the transverse bore in the first side of the bit skirt includes outer and inner portions, the outer portion extending from the outer surface of the first side of the bit skirt to an intermediate position between the outer surface of the first side of the bit skirt and the axial bore, the inner portion extending from the intermediate position to the axial bore; the transverse bore and the openings of the retainer tube each have an inside diameter and the pin has a substantially uniform outside diameter which is smaller than the inside diameters of the transverse bore and the openings of the retainer tube; the first end portion of the pin being disposed in the inner portion of the segment of the transverse bore in the first side of the bit skirt and the plug being fixedly mounted in the outer portion of the segment of the transverse bore in the first side of the bit skirt.
 19. The percussion bit assembly of claim 1 wherein the bit skirt has an outer surface; the receptacle is a transverse bore having a first segment extending from the outer surface on a first side of the bit skirt to the axial bore and a second segment extending from the axial bore to the outer surface on an opposite, second side of the bit skirt; the longitudinal member is a retainer tube having a lower end portion defining oppositely disposed, first and second openings; and the lateral member is substantially identical first and second pins; the transverse bore and the openings of the retainer tube each have an inside diameter; each pin having outer and inner segments; the inner segment of each pin having an outside diameter which is smaller than the inside diameters of the transverse bore and the openings of the retainer tube; the outer segment of each pin having an outside diameter selected for frictional engagement between the outer segment of the pin and the transverse bore; the first and second pins being disposed in the first and second segments of the transverse bore, the outer segment of each pin extending from the outer surface of the bit skirt to an intermediate position between the outer surface of the bit skirt and the axial bore, the inner segment extending from the intermediate position through a one of the openings of the retainer tube.
 20. The percussion bit assembly of claim 19 wherein the inner segment of each pin extends a distance into the bit bore.
 21. The percussion bit assembly of claim 20 wherein said distance is substantially equal to ¼ inch.
 22. A percussion bit assembly for downhole boring operations comprising: a percussion bit including an upper, elongated bit shank, a lower bit head, and a bit skirt disposed intermediate the bit shank and the bit head; the percussion bit defining an axial bore extending longitudinally through at least the bit shank and the bit skirt, the axial bore having upper and lower portions; the upper portion of the axial bore defining a circumferential shelf; the percussion bit also defining a plurality of circumferentially spaced receptacles, each receptacle extending radially outward from the lower portion of the axial bore; and a bit retainer including a plurality of retainer bars and upper and lower spacers; each of the retainer bars including a longitudinal segment and a lateral segment; the longitudinal segment extending longitudinally within the axial bore of the percussion bit from an upper end portion to a lower end portion; the upper end portion of each longitudinal portion having a tab extending radially outward therefrom, the tabs being supported on the shelf of the percussion bit axial bore; the lateral segment extending laterally from a radially inner end portion, connected to the lower end portion of the longitudinal segment, to a radially outer end portion; the outer end portion of a one of the retainer bars being disposed within each of the receptacles; the upper spacer being positioned proximate to the upper end portions of the retainer bars and the lower spacer being positioned proximate to the lower end portions of the retainer bars, whereby the upper and lower spacers prevent radial movement of the tabs and the lateral segments of the retainer bars.
 23. A percussion bit assembly for downhole boring operations comprising: a percussion bit including an upper, elongated bit shank, a lower bit head, and a bit skirt disposed intermediate the bit shank and the bit head; the bit skirt having an outer surface; the percussion bit defining an axial bore extending longitudinally through at least the bit shank and the bit skirt and a transverse bore having a first segment extending from the outer surface on a first side of the bit skirt to the axial bore and a second segment extending from the axial bore to a position intermediate the axial bore and the outer surface on an opposite, second side of the bit skirt; the axial bore having upper and lower portions; the upper portion of the axial bore defining a circumferential shelf; and a bit retainer including a retainer tube and a pin; the retainer tube extending longitudinally within the axial bore of the percussion bit from an upper end portion to a lower end portion; the upper end portion having a circumferential collar extending radially outward therefrom, the collar being supported on the shelf; the lower end portion defining oppositely disposed, first and second openings; the pin having a first end portion positioned in the first segment of the transverse bore, a middle portion extending through the openings of the retainer tube lower end portion, and a second end portion positioned in the second segment of the transverse bore; the bit retainer also including a pin retaining element.
 24. The percussion bit assembly of claim 23 wherein the transverse bore and the openings of the retainer tube each have an inside diameter; the first end portion of the pin includes outer and inner segments, the outer segment extending from the outer surface of the first side of the bit skirt to an intermediate position between the outer surface of the first side of the bit skirt and the axial bore, the inner segment extending from the intermediate position to the axial bore; the second end portion of the pin, the middle portion of the pin, and the inner segment of the first end portion of the pin have a substantially uniform outside diameter which is smaller than the inside diameters of the transverse bore and the openings of the retainer tube, and the outer segment of the first end portion of the pin has an outside diameter selected for frictional engagement between the outer segment of the first end portion of the pin and the transverse bore, whereby the outer segment of the first end portion of the pin is the pin retaining element.
 25. The percussion bit assembly of claim 23 wherein the first segment of the transverse bore includes outer and inner portions, the outer portion extending from the outer surface of the first side of the bit skirt to an intermediate position between the outer surface of the first side of the bit skirt and the axial bore, the inner portion extending from the intermediate position to the axial bore; the transverse bore and the openings of the retainer tube each have an inside diameter and the pin has a substantially uniform outside diameter which is smaller than the inside diameters of the transverse bore and the openings of the retainer tube; the first end portion of the pin being disposed in the inner portion of the first segment of the transverse bore; the pin retaining element being a plug fixedly mounted in the outer portion of the first segment of the transverse bore.
 26. A percussion bit assembly for downhole boring operations comprising: a percussion bit including an upper, elongated bit shank, a lower bit head, and a bit skirt disposed intermediate the bit shank and the bit head; the bit skirt having an outer surface; the percussion bit defining an axial bore extending longitudinally through at least the bit shank and the bit skirt and a transverse bore having an inside diameter, a first segment extending from the outer surface on a first side of the bit skirt to the axial bore, and a second segment extending from the axial bore to the outer surface on an opposite, second side of the bit skirt; the axial bore having upper and lower portions; the upper portion of the axial bore defining a circumferential shelf; and a bit retainer including a retainer tube and substantially identical first and second pins; the retainer tube extending longitudinally within the axial bore of the percussion bit from an upper end portion to a lower end portion; the upper end portion having a circumferential collar extending radially outward therefrom, the collar being supported on the shelf; the lower end portion defining oppositely disposed, first and second openings, the first and second openings each have an inside diameter; each pin having outer and inner segments; the inner segment of each pin having an outside diameter which is smaller than the inside diameters of the transverse bore and the openings of the retainer tube; the outer segment of each pin having an outside diameter selected for frictional engagement between the outer segment of the pin and the transverse bore; the first and second pins being disposed in the first and second segments of the transverse bore, the outer segment of each pin extending from the outer surface of the bit skirt to an intermediate position between the outer surface of the bit skirt and the axial bore, the inner segment extending from the intermediate position through a one of the openings of the retainer tube. 